1. Field of the Invention
The present invention relates to photovoltaic modules, and in particular to photovoltaic modules adapted for installation on roofs.
2. Brief Description of the Prior Art
The use of photovoltaic (“PV”) modules on roofs is becoming increasingly common. Often perched on tile or shingle-covered roofs, these solar energy-generating arrays are quite visible, and generally not quite aesthetically pleasant to the eye, somewhat comparable to the TV antennas of the past. To date the installations appear to have been motivated by purely practical, functional considerations; there generally appears to be little to no color and design coordination between the PV modules and the roofing tiles or shingles on which the modules are mounted.
PV modules usually feature a black to purple or blue surface protected by a thin transparent glass or plastic cover. These colors frequently do not work well aesthetically with the rest of the roof.
Photovoltaic materials require incident light to produce energy via the photoelectric effect. Such materials typically have a wavelength dependency in their response to incident light. That is to say that some parts of the spectrum may be used by a PV module more effectively than others in producing electricity. Intuitively, to cover or color the PV module with an opaque material to obtain a desirable aesthetic appearance would cause a blocking of the incident light and the photovoltaic material would no longer be active. To color the top surface with a clear coating, film or membrane may change the color, but may not easily yield a desirable effect for a roofing product. Also, a visually transparent film may still block parts of the spectrum important for power generation.
A variety of approaches have been taken for using the substantial area provided by roofs to collect solar energy. One approach has been to cover existing roofs using systems employing panels, tiles or shingles including solar cells. Panel-type systems are disclosed, for example, in U.S. Pat. Nos. 5,232,518 and 6,245,987.
Various attempts have been made to blend photovoltaic cells with traditional roofing systems. For example, U.S. Pat. No. 5,575,861 discloses a photovoltaic shingle system including a strip of roofing material having an overlap portion, with tabs extending from the overlap portion. Each of the tabs includes a photovoltaic device. U.S. Pat. No. 6,875,914 discloses a photovoltaic roofing system including photovoltaic power-generating roofing shingles provided with a linearly aligned electrical terminal. A protective cap shields the electrical connections. U.S. Pat. No. 6,883,290 discloses a shingle system including photovoltaic modules secured to a base to create a shingle assembly with a venting region between the module and the base for temperature regulation. U.S. Pat. No. 6,928,775 discloses a multi-use electric tile module for walling, flooring or roofing applications that can include a photovoltaic module. U.S. Patent Application Publication No. 2006/0000178 discloses a shingle assembly with a support bracket specifically adapted for the installation of photovoltaic shingles.
U.S. Patent Application Publication No. 2005/0102947 discloses photovoltaic building materials having a regular shape, such as rectangular or trapezoidal, and carrying solar cells formed from thin film materials, conventional crystal/silica, or photoelectric silica spheres. The materials are specially adapted for installation along the ridgeline of a roof. U.S. Patent Application Publication No. 2005/0144870 discloses a shingle system incorporating a photovoltaic module and a base to define a venting region, and may include a waterproofing element.
U.S. Patent Application Publication No. 2005/0178429 discloses flexible integrated photovoltaic roofing membrane shingles having a “dragon's tooth” shape with solar elements that connect electrically with previous and successive shingle courses. U.S. Patent Application Publication No. 2005/0263179 discloses a photovoltaic module architecture which includes electrical interconnects that provide for connecting the anode of one module with the cathode of another module.
U.S. Patent Application Publication No. 2005/0268962 discloses flexible photovoltaic cells and related systems. U.S. Patent Application Publication No. 2006/0032527 discloses a solar panel overlay and assembly for mounting on an underlying roof deck, designed to mimic the appearance of the underlying shingled roof deck.
U.S. Patent Application Publication No. 2003/0121228 discloses a dendritic web solar cell shingling system providing much thinner photovoltaic arrays than conventional cells.
U.S. Patent Application Publication No. 2006/0042683 discloses a system for mounting photovoltaic cells on a surface and for using the electrical energy produced. The cell can be pigmented to assure efficient collection of available radiation, for example, by using a pink-colored glass.
U.S. Patent Application Publication No. 2005/0048821 discloses a dye-sensitized solar cell having a high conversion efficiency.
U.S. Patent Application Publication No. 2003/0154973 discloses a radiation collector configured to collect incident radiation. The collectors can be colored to give the appearance of traditional shingles or other roofing or building material such that the roof appears aesthetically the same as a traditional roof.
U.S. Pat. No. 5,650,019 discloses a solar cell module having a three-layer structure including a thin film solar cell, a hard resin layer such as polycarbonate to mechanically protect the solar cell, an ultraviolet radiation absorbing adhesive layer to protect the hard resin layer, such as ethylene vinyl acetate including an ultraviolet absorber such as a suitable benzophenone or triazole, and an outermost layer having excellent weatherability, such as a fluororesin.
U.S. Pat. No. 6,331,673 discloses an amorphous silicon solar cell module in which the solar cell is encapsulated in a transparent organic polymer, namely an acrylic resin, and covered with a thin film of a suitable fluoropolymer resin, reinforced with glass fibers.
There is a continuing need for photovoltaic modules having more controllable and desirable aesthetics for use in roof applications while still maintaining sufficient efficiency in power generation.